Current actuators manipulate and position objects in single axis and multiple axes of orientation, altitude, and azimuth in various fields such as solar power, astronomy, satellite communications, RADAR, thermal imaging, construction, weapon deployment, and advertising. With respect to large scale or heavy equipment applications, current actuators employ gear drives, planetary gears, hydraulic pistons, pneumatic pistons, screw drives, and various clockwork machinery to position large and heavy objects around stationary mounts. Due to their reliance on electrical motors and various hydraulic means to move heavy and large objects, current actuators require large numbers of precision-engineered parts and a significant electrical power supply. Current actuators also require multiple heavy connections between structural members and actuators to support and position heavy and large objects. Hydraulic and electric drives require expensive hoses and cabling to transmit power. The heaviness and the precision metal-to-metal gearing and mechanics of current actuators dictate that normal metal fatigue, operational wear-and-tear and external stress, dust, contaminants, foreign objects, lubrication problems, and even minor operator errors and omissions create significant use-related damage, chattering, free play, and consequent degradation in accuracy and durability. Such actuators, which are also known as “clockwork” actuators, necessitate high costs of inspection, maintenance, repair, and replacement of precision-machined components, and consequent downtime from productive operations. Typically, the clockwork actuators do not provide a smooth tracking motion, but a periodic stepping motion common to the motorized systems.
Actuators are used in the collection of solar energy. Solar energy can be collected through the concentration of sunlight by aiming an array of mirrors such that they reflect sunlight into a single fixed receiver to produce concentrated heat for steam production. For an example of such a power plant see U.S. Pat. No. 6,957,536. The motion of the earth in rotation and around the sun in orbit necessitates a mechanism for aligning the mirrors or panels in a position relative to the sun as it moves across the sky on a daily basis and relative to the horizon on a seasonal basis so that solar energy is continuously reflected onto the receiver. Examples of solar collectors that provide single-axis tracking are disclosed in U.S. Pat. No. 4,135,493 and U.S. Patent Application 2008/0128017. Other solar collectors track the sun's motion in multiple axes. In practical terms, devices to constantly orient a collector or mirror toward the sun must provide a means for continuously adjusting azimuth (rotation around the horizon line) and altitude (rotation from the horizon to a position directly overhead) to continuously track the apparent motion of the sun through the sky.
Current solar energy collectors include devices that rotate in a single axis and multiple axes to maintain the desired orientation of a panel of solar cells and solar thermal collectors or mirrors throughout the day and year. These devices are referred to as “trackers,” “heliostats” or “positioning systems.” Thus far, current positioning systems are complex and expensive. Particularly as the size of the of the mirrors and photovoltaic panels increase to over 100 m2 on a single tracker, the complex precision gear drives and powerful motors required to maneuver and stabilize the panels (particularly in high wind conditions) have emerged as the largest single cost barrier in pursuing large scale solar power generation. These clockworks are delicate and prone to mechanical failure or degradation under normal and abnormal operating conditions. These and other limitations of current heliostat technology are among chief barriers to lowering the cost of electrical generation via solar thermal or concentrated solar energy to equal or below the cost of electricity from coal and natural gas-fired generating plants.
Other typical examples of the current heliostat technology include U.S. Pat. No. 3,070,643 disclosing a closed loop servo system for continuously pointing a solar cell directly toward the sun by sensing the sun's position and selectively driving the solar cell support about one or the other of a pair of axes. This patent discloses a complicated gearing system with a single drive motor and an electrically operated clutch to permit selective dual-axis drive. Another system, disclosed in U.S. Pat. Nos. 3,998,206 and 3,996,917, employs separate drive motors for obtaining dual-axis movement. The use of motor drives and gear reduction adds significantly to the cost of initial installation and maintenance of a sun tracking apparatus. In addition, the power required to drive the powerful motors creates a parasitic power drain on the operation of the solar power plant. The use of gear and motor drives is typical of the current actuators as disclosed in, by way of example, U.S. Pat. No. 6,440,019.
Another disadvantage of the current heliostat technology is its reliance, in most cases, on external sources of power. The current actuators require the provision of electrical or hydraulic power to orient the application. This generates a parasitic power drain on the installation, and also requires complicated and expensive electrical or hydraulic power distribution systems using cables or hoses for their operation. By their nature, heliostat arrays often cover many square kilometers, and thus, over a large installation, the provision of external power through cables to an array of thousands of heliostats adds to major capital and maintenance expense. The current actuators fail to achieve a low cost means of providing multi-axis sun tracking with minimal power requirements. Accordingly, there is a need for a cost and power efficient single and multi-axis actuator for use in small to large scale applications.
Current actuators' use of fluid pressure springs and incorporation of a piston and a flexible member that forms a rolling lobe as the piston reciprocates in operation is described in many patents such as U.S. Pat. No. 3,053,528, and in U.S. Pat. No. 4,378,935. These devices, in the form of a flexible membrane coupled to a piston, produce large amounts of motive force as they expand. While these devices may be used as actuators, they are mainly used as shock absorbers or springs on heavy machinery and vehicles, measured primarily by lifting capacity or compression and extension capacity. These devices have a very limited range of motion or play and very limited use for motion control requiring accuracy. These devices are not designed for controlled non-linear motion, rotary motion or arcuate motion, and exhibit little if any capability for such rotary motion or for control of such motion. Accordingly, there is a need for improved single-axis and multi-axis actuators.